In 1912, Alfred Wegner suggested that continents actually moved.
One reason for his suggestion was the remarkable fit between the
coastlines of South American and Africa (as shown in the figure
at the right*). This idea was rejected as implausible for half
a century.

As part of the moon program, a corner reflector was placed on
the moon. A laser beam bounced off this reflector would come right
back in the direction it came in from. A laser put through a telescope
at Goddard Space Flight Center in Greenbelt, Maryland (picture
at the right below**) was able to reflect the beam off the moon
and detect its relfection back again through the telescope. Accurate
measurements of the emission and reception time lead to very accurate
measurements of position.

Careful analysis of data from experiments like these lead to a measurement
of the drift rates of continents. Drift rates of a few cm per year have now
been measured for some points.

If we assume that the South American continent drifted away from Africa at
a constant velocity of 5 cm/year, estimate how many years it would have taken
to reach its current position.